The application of equal channel angular pressing to join dissimilar metals,aluminium alloy and steel,using an Ag–Cu–Sn interlayer

Joining cylindrical and bar-shaped components manufactured from dissimilar materials is frequently required in various industrial applications. The current study focuses on developing equal channel angular pressing (ECAP) as a severe plastic deformation process for solid state joining of tubular aluminium alloy 6061 components and SAE 1018 steel rods. The influence of using a 0.1 mm thick 60Ag–30Cu–10Sn interlayer in addition to annealing at 220, 320, 420 and 520 °C for 60 min is investigated as well. Finite element analysis (FEA) is performed in order to evaluate the deformation behaviour of the workpieces during the ECAP joining process. XRD and EDX analyses as well as nanoindentation and shear tests are carried out to evaluate the joints' characteristics. The FEA outcomes show remarkable accumulation of equivalent plastic strain with relatively low strain inhomogeneity. Moreover, the experimental results indicate that with increasing annealing temperature, joint strength exhibits improvement as well. It is also revealed that the application of an interlayer at any specific annealing temperature leads to achieving higher shear strength values. According to the results, shear strength of up to 32 MPa is feasible by having an interlayer and with subsequent annealing at 520 °C.     

Weak magnetic flux leakage: A possible method for studying pipeline defects located either inside or outside the structures

Magnetic leakage distribution results from linear defects of oil–gas pipelines in a weak magnetic field, which is modeled by the magnetic dipole theory. The analysis is useful for the identification of defects located either inside or outside the pipelines. The results indicate that the radial signals of inside–outside defects can be clearly distinguished, and the axial signals are basically the same in a weak magnetic field. The theoretical and the experimental results are very consistent.     

Fabrication of tungsten-based metallic glasses by low purity industrial raw materials

Quaternary W₃₀Fe₃₈B_32−xC_x (x = 5, 7, 10, 13, 15 at.%) alloys have been investigated by melt-spinning method to produce metallic glasses using low purity industrial raw materials. The phase structure of these ribbons is investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The thermal stabilities of W₃₀Fe₃₈B_32−xC_x (x = 5, 7, 10, 13, 15 at.%) alloys are analyzed by differential scanning calorimeter (DSC). It is found that W₃₀Fe₃₈B₂₂C₁₀ metallic glass with 45 μm in thickness and 2 mm width can be successfully fabricated. And other alloys with the same thickness and width as W₃₀Fe₃₈B₂₂C₁₀ alloy are observed with some crystalline peaks on the halo patterns. The DSC measurements show that each alloy undergoes a two-step crystallization with the onset temperature of the first crystallization being as high as 984-1067 K. Vickers hardness and density values of W₃₀Fe₃₈B_32−xC_x (x = 7, 10, 13, 15 at.%) alloys at room temperature are 11.9-12.8 GPa and 14.5 g/cm³ at least, respectively. The effect of C addition on GFA in the W-Fe-B alloy system is discussed.     

The effects of Co and Ti additions on microstructures and compressive strength of Udimet710

The effects of Co and Ti additions on the microstructures and compressive strength of the Ni-based superalloy Udiemt710 (U710) were investigated. The preliminary results showed that the Ni₃Ti-type (η) phase was observed in the alloys with low Co and Ti content; while a (Ni_xCo_1?x)₃Ti phase with a hexagonal structure was detected in the alloys with high Co and Ti content. The γ′ → η → (Ni_xCo_1?x)₃Ti phase transformation was discussed in terms of Co and Ti contents. The γ′ morphology changed from spherical to cuboidal with increasing Co and Ti content. Compressive tests showed that the alloys with Co and Ti addition possessed higher yield strength than the base alloy, U710. The strength increase could be ascribed to solid–solution strengthening of the γ and γ′ phases as a result of the Co and Ti additions, and the higher volume fraction of γ′ in the new alloys.     

Improving the mechanical properties of graphene oxide based materials by covalent attachment of polymer chains

We report on the modification of graphene oxide (GO) with poly(vinyl alcohol) (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration. Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150 kg/mol. Improvements in Young’s moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in PVA-based composites. The application of a pre-selection method allowed the use of only the largest functionalised f-(PVA)GO flakes. This resulted in substantially reinforced PVA–f-(PVA)GO composites. Both modulus and strength increased by 40% relative to the pure polymer for f-(PVA)GO loadings below 0.3 vol.%.     

Friction and wear of powdered composites impregnated with WS2 inorganic fullerene-like nanoparticles

The impregnation of inorganic fullerene-like nanoparticles of WS₂ (IF) allows to improve effectively the tribological properties of powdered materials in comparison to the impregnation of oil or commercially available layered WS₂ (2H) particles. The main goal of this work was to determine the dominant lubrication regimes under friction of the bronze, iron, and iron–nickel porous matrixes impregnated with 2H and IF solid lubricants. The tribological tests were performed at laboratory atmosphere (humidity ∼50%) using a ring-on-block tester at the sliding speed of V=1 m/s, and the loads of 150–1000 N. The wear of the metal bodies was measured by an eddy current probe system and by weighting of the samples before and after the test. In order to evaluate the radial clearance, the profiles of wear blocks were analyzed by profile projector. Than these data were used in the calculation of the Sommerfeld reciprocal values. Friction and wear results were presented as the Stribeck curves. The critical Sommerfeld reciprocals were evaluated from these curves. The Stribeck curves were compared with the Morgan’s curves for different ranges of non-dimensional permeability, Ψ. These results are used then in calculation of the permeability, Φ. Three lubrication regimes as: quasi-hydrodynamic, boundary or mixed, and dry friction were revealed under friction of porous samples in the load-range studied. It was found that the impregnation of IF nanoparticles provides the regime of quasi-hydrodynamic lubrication in the widest range of loads in comparison to the reference sample and the sample impregnated with 2H–WS₂. Fe–Ni samples exhibited the highest wear resistance and provided the widest range of quasi-hydrodynamic lubrication in comparison to bronze and iron powdered composites. The effect of IF on the regimes of lubrication is explained on the base of the third-body model. It is expected that the sliding/rolling of the IF nanoparticles in the boundary of the first bodies and in between the wear particles (third-body) facilitate the shear of the lubrication film and thus provide the quasi-hydrodynamic regime of friction. It is supposed that the roll shape of IF nanoparticles allows to release the IF from the pores to contact surfaces.     

The receptance sensitivity and the effect of concentrated mass inserts on the modal balance of spindle-bearing systems

In this paper, it is shown how the receptance of a modified system can be described in terms of the receptance of the unmodified system. Furthermore, a receptance sensitivity analysis is introduced to show the effects of design changes on the dynamic performance of vibrating structures. The spindle-bearing system is chosen as a good target for investigation with respect to machine tool's performance. The sensitivity analysis carried out shows the effect of concentrated mass inserrts on its dynamic behaviour.The concept of modal flexibility sharing is chosen as a good measure of modal balance of the vibrating structure. Therefore, a technique is introduced based on the aforementioned method to achieve such state of modal balance by means of some mass inserts. The results obtained lead one to think that such a procedure can be employed to optimise the vibration behaviour of structures in general and machine tools in particular.     

轴向迷宫密封性能的流固耦合分析

以往轴向迷宫密封设计时多借鉴旋转迷宫密封的研究成果,而对于轴向迷宫密封,其内部流体变化形式存在较大区别.为探讨轴向迷宫密封流场分布和泄漏特性,对某型号迷宫压缩机活塞气缸部位采用的齿形轴向迷宫密封结构进行研究.建立该轴向迷宫密封结构的三维模型,对迷宫密封泄漏特性进行流固耦合分析,分析迷宫密封流体域内压力分布、流场分布及结...     

HVOF喷涂Co基WC涂层的耐锌腐蚀行为

为了提高热镀锌用辊件的耐腐蚀性,试验采用超音速火焰喷涂方法制备WC-12Co涂层,研究了涂层在450 ℃锌液中的耐腐蚀性能以及失效机制.将316L/WC-12Co涂层进行液锌腐蚀,以扫描电镜能谱分析、x-射线衍射方式分析对比了未经过腐蚀试件、腐蚀5天试件、腐蚀10天试件的组织变化和相组成,结果显示涂层基体Co受液锌腐蚀生成Co与Zn化合物,引发横向裂纹,导致涂层剥落.涂层全部剥落后保护失效,使母材被液锌直接严重腐蚀,最终生成锌渣FeZn₁₃.